Enhanced thin film wiring net repair process

ABSTRACT

A process for partially repairing defective Multi-Chip Module (MCM) Thin-Film (TF) wiring nets. The process comprises the steps of locating a short circuit between any two nets of the MCM, identifying a site to cut in one of the two nets, and deleting an internal portion of one of the two nets at the identified site.

TECHNICAL FIELD

Field of the Invention

The present invention generally relates to thin film repair and, moreparticularly, to the partial repair of thin film wiring nets usingtop-surface-metallurgy (or TSM) repair lines.

BACKGROUND OF THE INVENTION

Conventionally, after an entire Multi-Chip Thin Film (MCM TF) module iscompleted, a full electrical test, an ATF test, is performed to confirmthe integrity of the completed wiring. If any defect is detected at thisstage, an after thin film (ATF) repair using top-surface repair lines isperformed to correct the defective nets.

FIG. 1 shows a plan view of a typical MCM 100. In FIG. 1, chips 102,104, 106, 108, 110, 112, and 114 are mounted to the top surfacemetallurgy (TSM) of MCM 100 using a Controlled-Collapsed-Chip-Connection(C4) configuration (not shown in this Figure). In FIG. 1 seven chiplocations are shown. MCMs are not limited to this configuration,however, and may be any number of chips depending on the requirements ofthe application. Before mounting the chips 102 through 114, MCM 100 istested to ensure that no open circuits or short circuits exist in MCM100. If open circuits or short circuits are found, the MCM must berepaired.

The conventional ATF repair strategy discards the entire original netwiring and reconstructs new net wiring using the top surface repairlines, modifying their lengths to match the required electricalproperties of the deleted wiring net. This conventional ATF repairmethod has worked well for traditional MCM-TF manufacturing. For tightground rule MCM-TF products, however, a drawback of this conventionalrepair process is that product yield is adversely affected if the numberof nets requiring repair exceeds the number of available repair nets onthe TSM.

Referring again to FIG. 1, a typical pair of wiring nets 116, 118 areshown. For illustrative purposes, it is assumed that a short circuitexists between wiring nets 116, 118. The conventional repair processdeletes the entire wiring nets 116, 118 by cutting wiring nets 116, 118at C4 location 120. In this example, wiring nets 116, 118 are cut (alsocalled deletes) at sites 122, 124, 126, 128, 130, 132, 134, 136, 138,140, 142, 144, 146, and 148. The deleted wiring nets 116, 118 must bereplaced using the TSM repair net (shown in FIG. 2A).

FIGS. 2A and 2B shows a typical TSM repair net 200 for the MCM ofFIG. 1. In FIG. 2A, repair net 200 is made up of x-lines 202 and y-lines204. As shown in FIG. 2B, within the gridwork of repair net 200 are C4connections 206 for each chip 102, 104, 106, 108, 110, 112, and 114mounted on MCM 100.

FIG. 2C shows an x-ray view of a five-layer MCM and FIG. 2D is a partialside view of MCM 100 illustrating the layered structure of MCM 100. InFIG. 2C, successive layers form MCM 100. Typical layers include groundlayer 208, power layer 210, x-layer 212, and y-layer 214. An additionallayer, top layer 216 (shown in FIG. 2D), contains repair net 200 and C4connections 206. It is apparent from FIG. 2C that repair of an internalshort circuit between any two x-layer lines or y-layer lines is aformidable task. For this reason, conventional repair processes deleteddefective nets at the top layer 216.

As mentioned above, conventional ATF repair is based on full repair.That is, the entire internal structure of a defective net is removed atits C4 connections 206. An entirely new set of wiring is reconstructedusing repair net 200 and connected to the C4 connections 206 on the TSM.These full repairs are necessary because frequently the location of thedefect in the defective net is unclear and the construction of a new netis the only practical way to repair the defective net.

FIG. 2E illustrates a portion of a typical MCM before repair. In FIG.2E, C4 connection 206 is connected to internal net 220 at via 238. Xrepair line 222 and Y repair lines 224, 226 are part of the top layer216. Y repair lines 224, 226 are connected by Y repair line subway 236using vias 228, 240.

The reconstruction of the net is normally accomplished by joining thesegments of the repair lines with individual gold slugs bonded to theTSM of the repair through conventional lasersonic bonding processes. Thegold slugs interconnect specific X and Y repair line segments to rebuildthe net topography.

FIG. 2F illustrates the conventional repair process mentioned above. InFIG. 2F, when a short is found in internal net 220 it is completelydisconnected from the circuit using external delete 230 between C4connection 206 and via 238. This process is repeated at every other C4connection location for internal net 220. To replace this deleted net, aportion of X repair line 222 and Y repair lines 224, 226 must be used.Conventionally, X repair line 222 and Y repair lines 224, 226 are cutusing deletes 232. Then C4 connection 206 is connected to X repair line222 and Y repair line 224 using gold slugs 234.

The drawback of this approach is that a relatively large number ofrepair lines are consumed for nets with multiple segments. Asillustrated in FIG. 2F, an X repair line and a Y repair line werenecessary to replace internal net 220. This results in fewer nets beingrepairable. An additional drawback of this conventional repair processis the scrapping of a part if an input/output (I/O) net is identified asdefective. This is because conventional repair processes can only repairtop-to-top signal nets while an I/O site is connected within the layersof the device.

Furthermore, because most defective nets run in the same generaldirection on the device, they require the use of the same top-surfacerepair lines. In such a case a part might be lost due tounroutability--insufficient repair lines to meet the repairrequirements.

SUMMARY OF THE INVENTION

In view of the shortcomings of the prior art, it is an object of thepresent invention to increase MCM TF device yields by using a partialwiring net repair process.

The present invention relates to a process for partially repairingdefective MCM TF wiring nets. The process comprises the steps oflocating a short circuit between any two nets of the thin-film device.After a short circuit is located, an internal site to cut (delete site)is identified in one of the nets, and only a portion of one of theshorted nets is deleted and repaired. This process is continued untilall shorts are identified and repaired. It is understood that thisprocess can also to repair open defects in the MCM TF.

The process further determines any cuts to the first net such that thetiming of the uncut net is not affected by antenna effects of theremaining portions of the first net. The present invention also relatesto a process for maximizing the utility of TSM repair nets by deletingand repairing only a minimum portion of a defective net. The presentinvention finally relates to a process for removing a portion of eachlayer above a portion of a defective net and deleting a section of thedefective net.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, but are notrestrictive, of the invention.

BRIEF DESCRIPTION OF THE DRAWING

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawing. It is emphasizedthat, according to common practice, the various features of the drawingare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity. Included inthe drawing are the following Figures:

FIG. 1 is a plan view of a typical MCM;

FIG. 2A is a plan view of a typical TSM repair net for the MCM of FIG.1;

FIG. 2B is a detailed view of a portion of the repair net of FIG. 2A;

FIG. 2C is an x-ray view of a portion of the MCM of FIG. 2A;

FIG. 2D is a cross-sectional view of FIG. 2C taken along the line2D--2D;

FIG. 2E is a plan view of a portion of an MCM prior to repair;

FIG. 2F is a plan view of a portion of the MCM of FIG. 2E after aconventional repair;

FIG. 3 is a cross-sectional view of an MCM prior to application of theprocess of the present invention for repairing the MCM;

FIG. 4 is a flow chart diagram illustrating an exemplary embodiment ofthe present invention;

FIG. 5A is a schematic diagram showing a step in the process of FIG. 4;

FIG. 5B is a schematic diagram showing a step in the process of FIG. 4;

FIG. 5C is a schematic diagram showing a step in the process of FIG. 4;

FIG. 5D is a schematic diagram showing a step in the process of FIG. 4;

FIG. 6 is a partial plan view of an MCM using an exemplary partialrepair process of the present invention; and

FIG. 7 is a plan view of an MCM illustrating an exemplary perforatingdelete process of the present invention.

DESCRIPTION OF THE INVENTION

Referring now to the drawing, FIG. 3 is a cross-sectional view of atypical MCM layered structure. In FIG. 3, layers are successively formedto fabricate MCM 100 over substrate 320, such as a ceramic carrier, inthe following order: power mesh layer 318, fourth polyimide layer 316,x-line layer 314, third polyimide layer 312, y-line layer 310, secondpolyimide layer 308, ground mesh layer 306, first polyimide layer 304,and TSM layer 302. It is understood that this arrangement of layers isexemplary and may be in any other order or may include additional layersdepending on design requirements of the MCM.

FIG. 4 is a flow chart diagram of an exemplary embodiment according tothe present invention. This embodiment employs a process to delete aportion of a defective internal net in an MCM. The process shown in FIG.4 is described below in conjunction with FIGS. 5A, 5B, 5C, and 5D.

Once a short circuit is identified between two adjacent y-lines iny-line layer 310, for example, a laser (not shown) is used to delete aportion of one of the shorted y-lines. At Step 400, the MCM is insertedinto the repair tool (not shown). At step 402, a first aperture 502 isformed (shown in FIG. 5A) in first polyimide layer 304. In the exemplaryembodiment, first aperture 502 has a 65 μm×65 μm area, although an areaof any size may be used depending on the topology of the MCM layers. Itis preferred that first aperture 502 be about 2.5× the pitch (line widthplus inter-line spacing) of the x or y lines. In this example, the linewidth is about 12.5 μm and the spacing is about 12.5 μm, resulting in a25 μm pitch. First aperture 502 may be formed using laser pulses havingan output power of about 1-2 J/cm². The number and duration of laserpulses varies depending on the thickness of first polyimide layer 304but may typically be between 10-20 pulses in order to expose the surfaceof ground mesh layer 306.

At step 404, second aperture 504 (shown in FIG. 5B) is formed in groundmesh layer 306. Second aperture 504 completely penetrates ground meshlayer 306 and exposes the top surface of second polyimide layer 308.Second aperture 504 has an area smaller than the area of first aperture502 and is preferably about 2× the pitch of the x or y lines. In theexemplary embodiment, second aperture 504 has a 50 μm×50 μm area. Secondaperture 504 may be formed using laser pulses having an output power ofabout 10-30 J/cm², with a preferred output power of 21 J/cm². The numberof laser pulses varies depending on the thickness of ground mesh layer306 but may typically be 1 or 2 pulses in order to completely removeground mesh 306 and expose the surface of second polyimide layer 308.

At Step 406, any residual metal remaining after creating second aperture504 is removed using between 5-10 laser pulses of 1-2 J/cm² eachdepending on the amount of residue remaining.

At Step 408, third aperture 506 (shown in FIG. 5C) is formed in secondpolyimide layer 308 to expose a desired portion of y-line layer 310.Third aperture 506 has an area smaller than the area of second aperture504 and is preferably about 1.45× the width of the x or y lines. In theexemplary embodiment, third aperture 506 has a 19 μm×19 μm area. Thirdaperture 506 may be formed using laser pulses having an output power ofabout 1-2 J/cm². The number of laser pulses varies depending on thethickness of second polyimide layer 308 but may typically be between10-20 pulses in order to completely expose the desired portion of thesurface of y-line layer 310.

At Step 410, internal delete 508 (shown in FIG. 5D) is formed in y-linelayer 310 to eliminate the short circuit between the adjacent y-lines.Internal delete 508 has an area smaller than the area of third aperture506 and is preferably about 1.2× the width of the y lines. In theexemplary embodiment, internal delete 508 has a 15 μm×15μm area.Internal delete 508 may be formed using laser pulses having an outputpower of about 10-20 J/cm². The number of laser pulses varies dependingon the thickness of y-line layer 310 but may typically be 1 or 2 pulsesin order to completely remove the desired portion of y-line layer 310without exposing any portion of the surface below y-line layer 310.

At Step 412, any residual metal remaining after creating internal delete508 is eliminated using between 5-10 laser pulses of 1-2 J/cm² eachdepending on the amount of residue remaining.

Although the process outlined above describes removing a short circuitfrom y-line layer 310, it is understood that a short in x-line layer 314may also be eliminated by avoiding cutting into the lines in y-linelayer 310 and forming an internal delete in x-line layer 314. In thiscase, additional process steps are necessary to form an aperture inthird polyimide layer 312 and an internal delete in x-line layer 314.

FIG. 6 illustrates a partial plan view of an MCM using the partialrepair process of an exemplary embodiment of the present invention. InFIG. 6, internal delete 600 is formed in net 220 to disconnect defectivesegment 604 from the non-defective portion 602 of defective net 220. Thepartial repair of defective net 220 is completed by connecting a portionof x repair line 222 to C4 connection 206 using gold slug 234. Thisexemplary repair process does not require using y repair lines 224, 226.Consequently, a fifty percent saving of available repair lines results.

As stated earlier, partial repairs use about half of the repair lines.Therefore, by using a partial repair process, more defective nets in anMCM may be repaired resulting in higher device yields. Partial repaircan also repair an I/O net if a defect occurs in a top-to-top portion ofthe I/O net.

The partial repair process according to another exemplary embodiment ofthe present invention further reduces repair net usage by performingperforating deletes. Perforating deletes use the concept that thedeleted segments need to be as small as possible to prevent the deletedsegment from creating antenna noise pick-up in the wiring net which isshorted to the defective segment of the partially repaired net.

There are certain acceptable segment lengths which are not prone tocause antenna effect. In a 5 nanosecond system, for example, a remainingsegment can be no more than 1 cm long to avoid antenna effect. Extensivefailure analysis has shown that there is greater than a 99% probabilitythat a defective net has only one defect (short) in the net. Therefore,based on this probability, repairing the second net is avoided bycutting the defective segment of the first net into multiple pieces,with each piece being shorter than 1 cm, for example.

FIG. 7 illustrates the perforating delete process. In FIG. 7, MCM 700has chips 702, 704, 706, 708 and 710 interconnected by wiring nets 712,714. For illustrative purposes it is assumed that a short is detected inwiring nets 712, 714 between chips 704 and 706 in segment 730 of wiringnet 712 and segment 732 of wiring net 714. Segment 730 is locatedbetween C4 connections 722 and 726. Segment 732 is located between C4connections 724 and 728. Segment 730 is disconnected from wiring net 712using deletes 716 and 734. Segment 730 is still connected to wiring net714 because of the short, however, resulting in antenna effect. Toeliminate the antenna effect, segment 730 is cut into smaller segmentsusing internal deletes 720 and 722, for example. In this example, thelength of any portion of segment 730 is smaller than 1 cm. This lengthis determined, as mentioned above, based on the operatingcharacteristics (i.e., timing, clock speed, etc.) of MCM 700. It is notnecessary to determine which portion of segment 730 was shorted towiring net 714 because the length of all portions of segment 730 aresmaller than 1 cm.

Perforation delete is useful to repair an I/O to non-I/O short. In thiscase, the non-I/O net is repaired and the portion shorted to the I/O netis perforation deleted. As a result, there is no need to repair the I/Onet.

Although the invention is illustrated and described herein withreference to specific embodiments, the invention is not intended to belimited to the details shown. Rather, various modifications may be madein the details within the scope and range of equivalents of the claimsand without departing from the invention.

What is claimed:
 1. A process for repairing a thin-film device having aplurality of nets, the process comprising the steps of:(a) locating adefect between any two nets of the plurality of nets, (b) identifying asite to cut in a first one of the two nets of the plurality of nets, and(c) deleting an internal portion of the first one of the two nets of theplurality of nets at the site identified in step (b), where only aportion of the plurality of nets remains intact.
 2. The processaccording to claim 1, wherein the first net forms a circuit and the siteidentified in step (b) is selected so that only a portion of the firstnet is disconnected from the circuit.
 3. The process according to claim1, further comprising the step of repairing the first one of the twonets using at least a portion of a repair wiring net of the thin-filmdevice.
 4. The process according to claim 1, wherein step (c) comprisesthe steps of:(c1) inserting the thin film device in a repair apparatus,(c2) exposing a first mesh layer within the thin-film device by removinga first polyimide layer from a first area on the surface of thethin-film device, (c3) removing a portion of the first mesh layer toexpose a second polyimide layer, (c4) removing the second polyimidelayer to expose a first wiring line, and (c5) cutting the first wiringline at the cite identified in step (b) to interrupt the first one ofthe two nets.
 5. The process according to claim 4, wherein the firstarea of step (c2) is a 65 μm×65 μm area.
 6. The process according toclaim 4, wherein the first area of step (c2) is about 2.5 times a linepitch of the plurality of nets of the thin-film device.
 7. The processaccording to claim 4, wherein step (c2) uses a laser having an energyoutput of between 1 to 1.5 J/cm².
 8. The process according to claim 4,wherein step (c3) removes a second area of the first mesh layer smallerthan the first area of step (c2).
 9. The process according to claim 8,wherein the second area is a 50 μm×50 μm area.
 10. The process accordingto claim 8, wherein the second area is about 2 times a line pitch of theplurality of nets of the thin-film device.
 11. The process according toclaim 4, wherein step (c3) uses a laser having an energy output between10 to 30 J/cm².
 12. The process according to claim 4, wherein step (c3)uses a laser having an energy output of approximately 21 J/cm².
 13. Theprocess according to claim 4, wherein step (c4) uses a laser having anenergy output of between 1 to 1.5 J/cm².
 14. The process according toclaim 4, wherein step (c4) removes a third area of the second polyimidelayer.
 15. The process according to claim 14, wherein the third area isa 19 μm×19 μm area.
 16. The process according to claim 14, wherein thethird area is about 1.45 times a line width of the plurality of nets ofthe thin-film device.
 17. The process according to claim 4, wherein step(c5) removes a fourth area of the first wiring line.
 18. The processaccording to claim 17, wherein the fourth area is a 15 μm×15 μm area.19. The process according to claim 17, wherein the fourth area is about1.2 times a line width of the plurality of nets of the thin-film device.20. The process according to claim 1, wherein the defect is a shortcircuit between the two nets.
 21. The process according to claim 20,further comprising the step of repairing the first one of the two netsusing at least a portion of a repair wiring net of the thin-film device,wherein the first one of the two nets is a non-I/O net and a second netof the two nets is an I/O net.
 22. The process according to claim 20,further comprising the step of repairing the first one of the two netsusing at least a portion of a repair wiring net of the thin-film device,wherein the first one of the two nets is a top-to-top net.
 23. Theprocess according to claim 1, wherein the defect is an open circuit inat least one of the two nets.
 24. The process according to claim 23,further comprising the step of repairing the first one of the two netsusing at least a portion of a repair wiring net of the thin-film device,wherein the first one of the two nets is a top-to-top net.
 25. A processfor repairing a thin-film device having a plurality of nets, the processcomprising the steps of:(a) locating a short circuit between a first netand a second net of the plurality of nets, (b) determining a timing ofthe second net of the plurality of nets, (c) identifying at least oneinternal site to delete in a portion of the first net of the pluralityof nets such that the timing of the second net is unaffected, and (d)deleting the at least one internal site of the first net identified instep (c), where only a portion of the plurality of nets remains intact.26. A process for repairing a thin-film device having a plurality ofnets using a repair apparatus, the process comprising the steps of:(a)inserting the thin-film device in the repair apparatus, (b) forming afirst aperture in a first polyimide layer of the thin-film device toexpose a first mesh layer of the thin-film device to expose a first meshlayer of the thin-film device, (c) removing a portion of the first meshlayer to expose a second polyimide layer, (d) removing the secondpolyimide to expose a first wiring line, and (e) deleting a portion ofthe first wiring line to interrupt a net of the plurality of nets, whereonly a portion of the plurality of nets remains intact.
 27. The processaccording to claim 26, further comprising, after the step (c), the step(c1) of removing residue formed in step (c).
 28. The process accordingto claim 26, further comprising, after the step (e), the step (f) ofremoving residue formed in step (e).
 29. A process for repairing athin-film device having a short circuit between two wiring nets, theprocess comprising the steps of:(a) determining a timing for each of thetwo wiring nets, (b) eliminating the short circuit by cutting a firstone of the two wiring nets in at least one location such that the timingfor the second wiring net of the two wiring nets is unchanged, and (c)repairing the first wiring net using only a portion of at least onerepair wiring net, where only a portion of the two wiring nets remainsintact, so that the timing of the first wiring net is unchanged.